fix Clashing endpoint-powered pages break route sorting(#4038)

[aolose]

issue #4038

fix:

1. shadow of shadowed page not change after merge matching page/endpoint pairs
2. fallthrough response didn't working at client-side （client-side don't know if the returned content is a fallthrough）
3. request from fallthrough shadowed page not match the right endpoint

update: 0e123e6

There are multiple fallthrough shadow page , like this:
[a] -- fallthrough -> [b] --fallthrough --> [c]
Before you need to request three times from client-side,
now you just need send one request.

update: 7397a20
add test :

1. client-side fallthrough from shadow page to another shadow page
2. client-side fallthrough from shadow page to another shadow page then fallthrough to no-shadow page

cd packages\kit\test\apps\basics
npx  playwright test -g 'Shadow fallthrough shadow'

Not in this Pr

update: a4a59f9 ~ d12479ec
merge from master

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpx changeset and following the prompts. All changesets should be patch until SvelteKit 1.0

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7397a20

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[Rich-Harris]

Thank you — I left comments inline. This PR will need some tests before we can merge it!

[Rich-Harris]

Thank you, but this will still need tests before it can be properly reviewed or merged

[Rich-Harris]

Can you undo the pnpm-lock.yaml changes please?

[Rich-Harris]

Thank you. I spent some time looking into this PR — unfortunately master has diverged quite a bit, so it isn't a straightforward merge. As explained in #4203 I think we need to use a simpler (if less sophisticated) implementation, since this is something of an edge case, so I'll close this in favour of that PR

[aolose]

Thank you. I spent some time looking into this PR — unfortunately master has diverged quite a bit, so it isn't a straightforward merge. As explained in #4203 I think we need to use a simpler (if less sophisticated) implementation, since this is something of an edge case, so I'll close this in favour of that PR

I agree width you, less sophisticated is better.